The short answer is that it's not a solvable problem. See Falsehoods Programmers Believe About Names for why that is.
If you insist on storing data labelled as first name and last name then the best plan is to ask the person for those data items as separate fields (ie. change your web form).
Are you posting in the right place? Check out Where do I post X? to know for sure.
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Want more info? How to link
or How to display code and escape characters
are good places to start.